Sheet media imaging systems include radiographic imaging systems which produce radiographic images on photosensitive sheet media such as film or paper. The photosensitive media is typically contained in a light tight cassette to facilitate handling and to shield the photosensitive media from exposure to external light. In film-screen analog radiography, the cassette includes one or two fluorescent screens which sandwich the photosensitive film in the openable, cassette. The cassette is positioned in back of the body part of a patient to be x-rayed. An x-ray source projects x-rays through the body part to irradiate the fluorescent screen(s) which emit a light image to produce a latent radiographic image of the body part in the photosensitive media. The media is then processed to produce in the media a visual radiographic image of the body part for observation and diagnosis.
Health imaging professionals require that diagnostic radiographic images be controlled within a narrow range of contrast and density to be acceptable. Because analog imaging uses direct x-ray exposures through a patient, retaking an image to get a correct exposure is undesirable, since it is expensive and time consuming and since it would expose the patient to more x-radiation. Where the radiographic sheet media is chemically processable, there is greater consistency in both the manufacture of the sheet media as well as the processing conditions of the media. Dry photothermographic media tends to be more variable in its manufacture and also tends to be more sensitive to the environment in which it is stored prior to use. These factors mean that the media density and contrast may vary unacceptably for the user. Laser imaged media can control its output simply by adjusting the intensity of the laser. In contrast, analog media is exposed from a variety of x-ray sources that cannot be easily controlled in an automated fashion. Thus, the image quality of dry photothermographic film may vary unacceptably unless a solution is found to reduce that variability. Sources of variability include manufacturing variability, media storage conditions such as humidity and temperature, age of the media, and ambient conditions at the time of processing the media.
The key to a successful processing system for heat processable photothermographic media is to ensure consistent output quality of the media, while not imposing additional workload on the users of the system. Adjusting the processing cycle allows the density and contrast of the media to be adjusted. One problem is determining what processing cycle to give each sheet of media. Since the sheets of media presented to the processor system may have multiple sizes, may come from multiple manufacturing lots, may be of different ages and have seen different storage conditions, each media sheet may need a different processing cycle.
Sheet media imaging systems also include laser imaging systems which produce medical images on photosensitive sheet film from digital medical images generated by diagnostic imaging systems (MRI, CT, US, PET), computed radiography (CR) systems, medical image digitizers, digital or analog medical image archives, direct digital radiography or the like. The sheet film can be packaged in optically opaque packaging which is removed under dark room conditions and loaded into a film supply of a laser imager. Dark room film loading is eliminated by the resealable film cartridge disclosed in U.S. Pat. No. 5,473,400 (Lemberger). The disclosed cartridge allows for daylight loading and can be reused and removed from the laser imager. U.S. Pat. No. 5,229,585 (Lemberger) discloses a bar code system which uses this resealable cartridge to control a laser imaging system. The cartridge has attached to it an optical bar code with a unique cartridge ID, film size, film type information and film sensitometric information. The laser imager has a bar code scanner which reads information from the bar code as the cartridge is opened. An imager management system controls the laser imager as a function of the input data and the information read from the bar code. A film processor develops the film as a function of film type information read from the bar code. The laser imager stores information relating to film usage of the cartridge.
U.S. Pat. No. 5,481,657, issued Jan. 2, 1996 (inventors Schubert et al.), discloses a multi-user digital laser imaging system wherein a calibration process is used including laser exposing a calibration film to a range of density patches, processing the film, measuring the density patches with a densitometer, comparing the measured densities with expected density values of a stored film model for the film, and modifying the film model if any discrepancies are noted.
U.S. Pat. No. 6,710,891 B1, issued Mar. 23, 2004, inventors Vraa et al., discloses a sheet media imaging system including a laser imager configured to operate with a resealable media cartridge having an RFID transponder storing relevant digital data that communicates with a laser imager transceiver.
U.S. Pat. No. 6,023,285, issued Feb. 8, 2000, inventors Kocher et al., discloses a photothermographic laser imaging system including a laser printer for exposing photothermographic media to digital data, a thermal processor for thermally developing the exposed photothermnographic media to render a visual image of the digital data and a densitometer for reading the density of the visual image. A method for establishing calibration of the system includes reading optimum thermal processing parameters including processor temperature from a bar code associated with unexposed photothermographic media; setting the thermal processor to operate at the read parameters; exposing a multiple step gray scale pattern calibration media by the laser printer; reading with the densitometer the densities of the multiple step gray scale pattern from the developed calibration media; and adjusting the temperature of the thermal processor if the measured densities are not within desired limits. (See also: U.S. Pat. No. 6,020,909, issued Feb. 1, 2000, inventors Kocher et al., and U.S. No. Pat. 6,223,585 B1, issued May 1, 2001, inventor Krogstad.)
U.S. Pat. No. 5,757,021, issued May 26, 1998, inventor Dewaele, is of interest in disclosing an identification system for use in the field of digital radiography including a cassette carrying a photostimulable phosphor screen which has an RF tag provided on the cassette. Patient identification data and examination type are stored in the RF tag by a health care provider and after the screen is exposed to an x-ray image, the RF tag and phosphor screen are read out and the radiation image is digitally processed in accordance with image processing parameters associated with the examination type and stored in the readout device. The RF tag is then erased.
Although the foregoing patents disclose systems that may have been useful for the purposes for which they were intended, none of them solve the problems discussed above relating to controlling image quality in processing x-ray exposed radiographic media, especially heat processable photothermographic media.
There is thus a need in a sheet media imaging system for a system for controlling image quality in processing x-ray exposed radiographic media, especially heat processable photothermographic film, which ensures consistent quality output of the media, while imposing minimal workload on the users of the system.